It is oftentimes necessary to purify the waste waters from meat, poultry, and other food processing plants, as well as from feed lots, in a special manner because of their high organic content. Present methods in use include the use of continuous or batch fed lagoons having anaerobic microorganisms contained therein. This type of process generates large quantities of gas which have extremely offensive odors. In order to complete the metabolic destruction of the suspended organic material in a reasonably short period of time, it is desirable to have the water at a temperature which is higher than the typical ambient outdoor temperature. The most economical method of maintaining an elevated temperature is by retention of the heat normally present in processed waste water and the heat generated by the bacteriological process. This can most readily be accomplished by some form of surface insulation on the surface of the waste water contained in the lagoon.
Insulation currently used are synthetic foams such as styrofoam or polyurethane. These materials in the foam form will float upon the surface of the water and will provide a reasonably low coefficient of heat transfer.
A second insulation in common use is a scum layer associated with certain meat packing operations. The scum layer is developed by beef processing waste waters and is limited to such wastes, as only these waters contain the materials which will both float and develop a scum.
The use of styrofoam or polyurethane foam insulation is relatively expensive and introduces a material into the environment which is not readily biodegradable. The scum layer method is inexpensive but is only available for beef processing waste waters and is a less efficient heat insulator than foam insulation. As a further disadvantage, neither of these types of insulation will absorb or adsorb any odors generated by the anaerobic bacteriological process.
The severe odor problem which is inherent in the anaerobic lagoon treatment method greatly limits the possible locations for treatment sites and creates a severe environmental problem.